This invention relates generally to drillhead units and particularly to a drillhead unit used in conjunction with a hollow drill bit to provide holes for the insertion of roof bolts in coal mines.
There are several problems connected with the drilling of holes in coal mine roofs for the insertion of roof bolts, particularly when drillhead units are used of the type which rely on a vacuum pulled through a hollow drill bit.
One of these problems is the relatively short life of the drillhead unit resulting from the fact that the vacuum used to remove cuttings from the hollow drill bit tends to suck the lubricant out of the unit which results in failure of the bearings and pinions.
Another problem is that when the hydraulic motors, which are used to drive the pinions, are changed due to malfunction dirt enters the drillhead unit and can cause premature failure. In general, drillhead units provide a beveled pinion mounted to the motor shaft, and when the motor is inserted into the pinion housing it automatically positions the pinion. This arrangement tends to lead to sealing problems and, in addition, in some cases, only the tips of the cooperating pinions in the drillhead are engaged due to an improperly located motor pinion and this can also result in wear and premature failure.
Still another problem is that the chuck depth for the hollow drill bit must be sufficient to provide a secure connection for the drill bit, so that it cannot be thrown out of the chuck during rotation, and this can result in the chuck extending a substantial distance above the drillhead unit.
Yet another problem with known drillhead units resides in the fact that the top surface of the housing is normally covered with dirt which migrates into the top seals because of inadequate sealing of the gear assembly of the unit operating in powdered coal and rock which is very destructive to the mechanism.
This drillhead unit solves the above and other problems in a manner not disclosed in the known prior art.